Electromagnetic losses causing undesired heating represent a well-known problem during the operation of electrical machines, such as generators or the like. The heating may lead to lowered efficiency or even to damage or a reduction of the lifetime, particularly the insulation lifetime of the electrical machine.
Hence, it has been proposed to cool the stator stack by blowing a gaseous cooling medium such as air for instance through the ends of the stator windings, that is the end windings into the air-gap between the stator and the rotor and additionally through radial duct-like channels, which are usually provided by means of so called spacers.
The spacers are generally of a rectangular shape and disposed between two or more adjacently disposed metal plates, that is when considering a top-view of the stator the spacers are usually arranged “in the middle” of two successive stator windings. Thereby, the spacers provide a certain gap between two or diverse groups of adjacently disposed metal plates since they provide a free volume through which a gas may flow in order to cool the stator windings and the surrounding stator lamination. Thus, on the one hand the spacers increase the gas flow in the radial duct-like channels, whereas on the other hand the pressure drop within the duct-like channel is increased due to the mentioned arrangement of the spacers inhibiting a desired gas flow through the stator. Generally, the metal plates may comprise a ring-like shape or in the case of a segmented stator the shape of a ring-segment.
Aside, so called pinpoint-spacers may be randomly distributed in between the stator stack or the stator lamination in order to withstand the axial pressure of the stator lamination. Likewise, pinpoint-spacers may further increase turbulence.
Yet, the given means may not always assure proper or sufficient cooling of an electrical machine, in particular as the known arrangement of spacers may negatively affect the flow of the gaseous cooling medium as mentioned above.